This application is a 35 USC 371 application of PCT/DE 99/04116 filed on Dec. 28, 1999.
The invention relates to a piston pump which is provided for use in a slip-controlled, vehicle hydraulic brake system.
Piston pumps of this kind are known in and of themselves. By way of example, reference is made to DE 41 07 979 A1. The known piston pumps have a cylindrical, pin- or bolt-shaped piston which is guided so that the piston can move axially in a pump housing. The piston can be guided directly in a pump bore in the pump housing, or a liner is inserted into the pump housing, with the piston guided inside the liner in an axially mobile fashion. The piston can be driven to execute a reciprocating stroke motion by means of a rotary-driven cam and this reciprocating stroke motion produces the delivery of fluid in an intrinsically known fashion, wherein with the provided use of the piston pump in a hydraulic vehicle brake system, the fluid is brake fluid.
In order to control a direction of a fluid flow through the piston pump, the known piston pumps have an inlet valve and an outlet valve, usually in the form of spring-loaded check valves.
In the piston pump according to the invention, at least one of the valves which control the through flow direction through the piston pump is replaced by a piston seal, which seals the piston in the pump housing or in the liner. The piston seal can be affixed to the piston or can also be affixed in a stationary fashion in the pump housing or the liner. The piston seal according to the invention is embodied so that the piston seal simultaneously functions as a check valve. The piston seal has a circumferential sealing lip which rests inside the pump bore of the pump housing, inside the liner, or against the piston. The fluid to be supplied acts on the sealing lip on both sides, wherein a pressure difference in one direction results in the fact that the sealing lip is lifted away from the pump bore, the liner, or the piston and the fluid can flow past the piston seal, whereas a pressure difference in the opposite direction presses the sealing lip against the pump bore, the liner, or the piston so that the sealing lip produces a seal. The piston produces the alternating pressure difference by means of its reciprocating stroke motion for delivering fluid.
The piston pump according to the invention has the advantage that at least one valve that controls the flow direction through the piston pump is replaced by a piston seal which is required anyway. It is therefore possible to eliminate a check valve, which includes a valve closing body, a valve closing spring, and a valve seat and whose parts must be manufactured and assembled. The piston pump according to the invention has fewer individual parts and the number of assembly steps required to assemble the piston pump is reduced.
Advantageous improvements and updates of the invention disclosed are the an object of the invention.
As set forth herein, the sealing lip is truncated, hollow, and conical; the sealing lip has the shape of a hollow cone, wherein the cone preferably tapers in the direction of its free edge. This shape of the sealing lip permits the desired flow past the sealing lip in one direction and produces a reliable seal in the opposite direction, even at high pressure.
According to one embodiment, the piston is embodied as a hollow piston; a displacement chamber of the piston pump, whose volume is compressed and expanded during the reciprocating stroke motion of the piston and as a result, produces the fluid delivery in an intrinsically known manner, is disposed inside the piston. This embodiment of the invention has the advantage that because the displacement chamber is accommodated inside the piston, the piston pump is small, in particular short in the axial direction. This embodiment of the invention allows the piston pump to be compact in structure.
In an embodiment set forth herein, a stationary inner part inside the pump housing protrudes into the piston, which is embodied as a hollow piston. The piston can move axially on the inner part. The inner part defines one end of the displacement chamber inside the piston. The displacement chamber is sealed by means of the piston seal, which is affixed to the inner part or to the inside of the piston and rests in a sealed fashion against an inside of the piston or against the inner part.
Preferably, the piston seal is of one piece with the inner part; the inner part including the piston seal is manufactured in one work cycle, for example in the form of an injection molded part made of plastic. This further reduces the manufacturing cost and the number of individual parts.
The piston pump according to the invention is provided as a pump in a hydraulic brake system of a vehicle and is used in the control of pressure in wheel brake cylinders. The abbreviations ABS, ASR, VDC, or EHB are used for such brake systems, depending on the type of brake system. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to supply brake fluid from a storage tank into a wheel brake cylinder or a plurality of wheel brake cylinders (ASR, VDC, or EHB). The pump is required, for example, in a brake system with wheel slip control (ABS or ASR) and/or a brake system serving as a steering aid (VDC) and/or an electrohydraulic brake system (EHB). With wheel slip control (ABS or ASR), for example, a locking of the wheels of the vehicle during a braking event when there is strong pressure on the brake pedal (ABS) and/or a spinning of the driven wheels of the vehicle when there is strong pressure on the gas pedal (ASR) can be prevented. In a brake system that serves as a steering aid (VDC), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the path desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump supplies the brake fluid into the wheel brake cylinder or cylinders if an electrical brake pedal sensor detects an actuation of the brake pedal or in which the pump is used to fill a reservoir of the brake system.